Planographic printing plate having a fibrous alumina coating thereon



v PLANOGRAPHIC has been coated with a hydr'ophih aluminum oxide pigment in-a film forming "material and "then coated withta thin film of a material suchas a photosensitive diazocompound which on exposure to actinic light is transformed: from a watersolublesubstanceinto 'a water insoluble substance. The plate is then developed I by washing with water which removesthe water' soluble photosensitive-diazo compound, in the places-where it has not been hardened by exposure to actinic "light...

Printing {is then effected from ajrnoistenedf plate using an oil-y" ink which ,adheres only to the portions Jwhere the was hardened and therefore PRINTING I FIBROUS.ALUM1NA"COATING. THEREON J" Robert H. Steinle, Middletown, Conn; assignor'to Sperry Rand Corporation, New York; N.Y.,.a corporation of Delaware g 1 v v NoDrawing. Filed June 24", 1963,Ser.-No. 290,166 1 8 Claims. .(Cl. 96-75) graphic printingplate andto a method of producing... it'.

LATE, nAvrNo A" n te States Patento r y 3,208,849 Patented Sepi 28,.19d5

'sirabl'e propertyiof 'reasonable,storage time after exposure and running on the press withbut'toning up.

Inpmducin'gthe platesof the present invention, bright I aluminum oronly very lightly etched-aluminum" plates are degreased, ,a necessary prerequisite to making any metaliplanogra'ph'ic plate and then} are coated with a very thinjdispersionof colloidal alumina,; .f orexample' a dispersion of fibrous alumina monoh'ydrate described in .Planographic printing plates'have been prepared before using a number'of substrates} Forexample, paper oleophilic diazo compound remained;

- Plates made from paper ,or "othermaterialsof limited e c'oatin'g suchv as an the Bugosh patent; US. 2,915,475. In this patent there.

is discloseda fibrousj'alumina monohydratehaving-the boehmite crystal latticeand made up ofalumina fibrils whichhave a surface ar'eaof250, to 350 m. /'g. and an average length of 100 to 2,0 ,00 millirnicro'ns and having an axialratio greater'than' :1. The coating is effected very simply at low temperatures, for example room tem ,perature'f'b'y conventional mechanical meanssuch as a roller or by swabbinga ,This is-an important practical advantage.inmanufacture as it is -not necessary to maindimensional. stability have not'provento be prarttitial.forfv high grade work and"me tal*.plates have therefore. been used'for many years in 'the pastJThes'e metal-plates were ordinarily made'from zinc by etching 0r graining the zinc plate to roughenitland then appiying alhydrophilic coating and a light. h'arden'able substance {as de-, scribed above. T hoseplates have given satisfactory ressults b'ut'hav'e a number of drawbacks;"The mo'st'ser'h ous, o'neis that they are not presensitized, that is to say they must be sensitized iinmediatelyprior to use, which 'seriouslyflcomplicates the production'of exposedjplatesi Alsoifor the very finest work 'the .etchingior gl'ainingproduces a surface-which i's'too rough to give maximum resolution of fine-detail,'fdrexarnple, in half tone work.

It was these serious drawbacks which led to attempts to I ta'in extremely precise film thickness by very sharply controlled coating-processes as was required with the aluminu 'rn plates heated with silicates referredto above The coating is, quickly insolubilized by drying; fora very short period: of t-inre at an elevated't'emperature. Neither time .nor temperature'is critical and 'typically the time may be less than 'ami'nutegfor exam'plep'abo'ut seconds with temperatureslranging from 100 to 120 C; or slightly higherf Af permanently'hydrophilic coating results which is highly. resistant to abrasion, and wea'r; ,The coated aluminum sheet is then buffed or otherwise treated to remove any excess coating leaving only an extremely,

thin layer adhering-sip the aluminum. flTh'e-"coating adheres with great tenacity to the aluminum and it is possible that there maybe'some chemical reaction though this isn'otlknowng The surface is not bright and shiny but israther dull; without however having any deep indentationsas in the case of grained zinc plates.

The aluminum plate with the extremely thin, smooth 'coating of the water insolublealuminais then sensitized by immersing ina photosensitive material such as photosensitive diazo' con1pound which adheres to the thin aluminacoating *This is followed again by a quickdrypreparop esensitized Plates which-could be 'sto'red for' a reasonabletime. and then used. T his led to the attempts described above 1 by using substrates other than metal.

Finally, there was produced a ine-tallicp're'sensitized' plate described in Patent 2,714,066.- This plate used 7 smooth aluminum, altho'ugh it. could be lightly etched if desired, coated with a layer of silicate, for vexample,

from alkali. metal'silicate solution,-and then the photocoating. -The plates produced had reasonable shelf-life been exposed and used for the printing itisl-desirable to be able to removethe ink and then store the pl'ateffor a reasonable period of time so that a.further ,runcan-be made, With the plate described above this is not practical and the instructions with the plate require that'in such sensitive diazo compound coated onto'this hydrophilic .50

I before'runnin'g oil? the prints;-

ing at'elevated temperature. The plate is then ready for packaging-in light=type containers in which form it is storage. stable- .-f o r long periods-of time and is ready for'exposu'fr'e and development by washing of the portions of the-photosensitive diazo compound which have not been insolubilize'd by actinic light.- If desired the image mayflbe developed or made visible by suitable colored lacquers so thata more precise registration can be obtainedyduring. printing.- and so that the pressmenmay determine whether the plate is, satisfactorily exposed As has been pointed out above, the exposed plate can be' stored for considerable periods of time which are frnor'ethan suflicient for the ordinary delays between exposure and printing. No special treating process is necessary and no protective layer needs to be washed off before printing.

a'case the surface of the plate must be treated with a 7 solution of gum a-rabic which is then buffed dry.- This involves additional treatment if the plate is tobe stored.

The present invention producesplates on. aluminum which is not deeply grained initially and may be quite bright. The plates are presensitized and} after exposure development and printing the ink can be removedand solution. All this obtained in addition to its very de without further treatmentthe plates can be stored from The late's of the present invention may be sensitized with a coating of the familiar albumin-ammonium dichromate type." However, photosensitive diazo compounds are preferable as the coating has greater stability and requires less exposure to actinic light through a negative. Asa result this isthe preferred modification of the presentinvention and is the one which is described in the specific examples in which the proportions are by weight unless otherwise specified.

Example 1 A sm'ooth sheetof aluminum, of .005 inch thickness, is prepared for the coating operation by degreasing with toluene. or other -suitable solvent. Following the de- 

1. A PRESENSITIZED PLANOGRAPHIC PLATE COMPRISING IN COMBINATION, A DEGREASED ALUMINUM SUBSTRATE, A HARD, ADHERENT, THIN FILM LAYER CONSISTING ESSENTIALLY OF WATER-INSOLUBLE FIBROUS ALUMINA HAVING THE BOEHMITE CRYSTAL LATTICE STRUCTURE ON THE PLATE, AND A LIGHT-SENSITIVE COATING ON THE LAYER OF SAID FIBROUS ALUMINA. 